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Old 18th July 2011, 10:55   #1
thomas.hood
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Which temperature sensor (coolant temperature implausibility etc.)

Hi,

IIRC there are 4 temp sensors on the S62:
1. MAFs - Inlet Air
2. Thermostat - DOUBLE TEMPERATURE SWITCH 13621703993
3. Top of Radiator hose - Coolant Temperature sensor 13621433077 (seems to be generic part across all BMWs)
4. Bumper - ambient temperature.

As far as triggering the 'engine temp coolant temperature implausibility' code, are only the first two relevant?

I replaced my MAFs and thermostat a while back with original parts. Previously the code would be thrown regularly, and this initially appeared to fix the issue (much quicker warm up, temperature didn't drop at cruise), but I still get the code sporadically.

Thanks,

Tom

Last edited by thomas.hood; 18th July 2011 at 11:06. Reason: added links
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Old 18th July 2011, 11:58   #2
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As far as sensors go, only number 2 is applicable to plausibility errors Tom. The only real other thing that sets this off is the stat itself which you have changed.
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Old 18th July 2011, 12:34   #3
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Temp plausibility code is exactly what it says.

It does not mean you have a temp problem, usually low temp, but it means you MAY have a low temp.

It is kind of a red herring in my opinion, kind of not a real code. Usually shows up with other codes like Cats Below Efficiency.

The temp sensor on top of the T-stat is the dual sensor that feeds the DMW and displays the coolant temp on the dash, they do have issues from time to time, are VERY easy to change and cost less than $25 as I recall.

If you are getting temp plausibility codes with other codes, ignore the temp plausibility for now.

Use #7 on the hidden OBC menu and watch the coolant temps closely. Not sure you locate temps, but even with a cooler 70 F outside air temp, my coolant temp it up to 79C within 3 miles on a non stop drive.

Let us know if you have other codes along with Temp Plausibility, I assume you have other codes at a minimum pending?
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Old 18th July 2011, 14:16   #4
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I think the DME has noted that your engine has been running for x miles and/or y time, and in this distance/time it should be fully warmed up, yet the Temp Sensor is not also reporting a fully warmed up scenario....hence the lack of plausibility, which more often than not is caused by a weak or failing/failed T Stat.
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Old 18th July 2011, 14:56   #5
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M5 London may have some insight, however, I do not think anyone other than the DME programmers really know what triggers the Coolant Temp Plausibility code?

I had just replaced my thermostat in the Winter and was actually watching my temps like a hawk as I was curious to see how the car temps behaved in the very cold weather. My coolant temp sensor was replaced a few months before I changed the stat by the prior owner, so it was relatively new. I actually had the OBC hidden menu temps up while driving for a 2-3 week period all the time. Car was fully warmed up and I was driving on a 55 MPH stretch with slight downhill grade for about 3-4 miles, then came to a stop. Took off from the stop and bang, CEL/MIL light comes on.

Get home and check the codes, Coolant Temp Plausibility and Cat Inefficiency codes. I call 100% BS on this as I was watching the temps for weeks and really closely just before the code was triggered. Turns out that I have slight post Cat exhaust leak causing Cat Inefficiency codes. I believe the way the DME is programmed, it may trigger Coolant Temp Plausibility for certain situations where the engine may not be warm enough, like Cat Inefficiency??

So before you get too concerned, watch OBC hidden menu #7 closely and see if you have any other codes either pending or triggering at the same time.

Just be careful not to believe everything you see as far as CEL/MIL codes, many times they are not 100% accurate, but may give you an idea as to what is up. My Cat Inefficiency codes are due to a slight post Cat exhaust leak, not bad Cats. Search the Internet and you will see countless Cats being replaced on these cars and many other non BMW's and the codes do not go away. Many times 02 sensors, minor exhaust leaks and exhaust mods cause these codes.
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Old 18th July 2011, 16:14   #6
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Kumaran is spot on. Certainly on cars around MY2000 this is often accompanied by the temp gauge maxxing out way past the red also. You can simply turn off the ignition and restart where it usually returns to normal readings.

If you are monitoring KTEMP on the OBC hidden menu at this time you'll see the reading jump from circa 70C or whatever its at to -168C IIRC thus giving the plausibility error.

FWIW mine maxxed out at the same point on my journey to work every day, give or take a few hundred yards, showing its pretty much a time constrained measurement by the DME.

I changed my temp sensor which cured the symptom for a few days before swapping the stat out which has eliminated it altogether
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Old 18th July 2011, 17:22   #7
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I would agree the next step would be to go after your #2 next would #4 because it plays a role in this also. #1 also plays a role but only as a backup, it appears to be responsible for outside air temp when 4 fails. I have this scenario going on in my car now. I have been watching test 7 Atemp (push left button 3 times). If you compare the outside temp normally displayed on your dash to that and see the the Atemp (maf air temp) dragging the outside temp down with it you have a bad outside air temp sensor.
Example would be I pull to a traffic jam outside air reads 30c Atemp climbs at my standstill to 43C. Traffic breaks and I move at 100kph again outside air reads 30c, Atemp starts coming down, when it gets to 30C it is the same as outside air, but the real temp is 24C. So as the car continues at speed the Atemp is no longer heat soaked and starts reading a temp close to the real temp. As it reads 24C the correct temp you will see both outside air and Atemp drop at the exact same time as it gets to the temp.
Jfoj that was for you as I read a description you posted having to do with air temp that lead me to the fault in my car, thanks, I am guessing your car behaves the same so you also may have a bad outside air like me. Specially if you got 69 a few times. I have not, but also did not even with a bad T-stat, I am guessing but think it may have to do with this.

Back to the OP more than likely it is #2 as it is the most common but you may want to do the same check. Here are the perimeters for the 69 The definition is for a Pcode and is only partially compete but gives a idea. 69 is only the rationally check of the p code. Concidering the relationship between the two air temp sensors it would not surprise me if somehow #3 plays a backup role for #2 somehow. I have found no reference to it.
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Edit: Sorry can't seem to post the other part that shows that the temp gets compared to outside air. or rather is dependent on out side air temp. Keeps showing stolen instead of the words

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Old 19th July 2011, 08:59   #8
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Maybe someone mentioned this but seems a implausibility code would simply indicate that the two sensors (double sensor) in the T-stat housing simply disagree w/ each other due to one being (or going) bad. The computer then displays the most probable/plausible temp reading on the user display. Two sensors being employed as a fail safe system because afterall we are cooling a $20k engine here and it would make sense to have a redundant feedback circuit to the DME. If only one sensor was used and was failing, you may never be made aware that your engine was destroying itself if other cooling components were also failing. Implausibility error will most likely be cured with a T-stat sensor change.

IIRC the sensor in the radiator hose sensor is basically a trigger for the pusher fan.

I could be wrong but that seems plausible to me. Sorry for the pun. Again I'm not 100% on this and I doubt anyone but a BMW engineer is.

Last edited by JDMM5; 19th July 2011 at 09:16.
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Old 19th July 2011, 11:23   #9
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Why does every documented fault on here have to be dissected and blown up into a mammoth PhD level discussion?

For over 99% of cases the fault will be triggered for exactly the reasons cited by Kumaran. That being, the coolant isn't up to temp after x amount of time, which is either due to the temp switch itself, or the stat.

Guys, we all appreciate the vast tech knowledge on here, certainly i do very much, but sometimes the simplest things get so muddied by vast amounts of tech talk and hypothesis that simply aren't needed.

There are many threads on the subject of this and i can only remember 1 poster not having permanent joy regarding this code or the gauge maxxing out by replacing the stat or the stat switch.

Of course if you have accompanying codes then sometimes not everything is as simple, but again there isn't a mention of this anywhere by the OP and we are all too eager to start jumping the gun sometimes.

In 8 posts its been suggested it's MAF's, Bad CAT's, an exhaust leak, the radiator pusher fan sensor, the outside air temp sensor (really?), and also the temp sensor itself and the stat. Genuine LOL's
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Old 19th July 2011, 11:35   #10
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3 things play a role regarding the coolant plausibility.

The t-stat as actor,the temp sensor on top of it as well as the one in the lower radiator hose which measures radiator outlet temp.

This is all information needed to understand how the code is triggered.
Do not feel like writing an essay how the MSS52 works for the exact reasons Jamie stated.


Had an S62 that had new t-stat and double switch sensor,still triggered plausibility code.
Changed lower radiator hose sensor,fine.

If double switch sensor and t-stat are working,change lower hose sensor.
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